Pradipkanti L, Chowdhury Mithun, Satapathy Dillip K
Soft Materials Laboratory, Department of Physics, Indian Institute of Technology Madras, Chennai - 600036, India.
Phys Chem Chem Phys. 2017 Nov 8;19(43):29263-29270. doi: 10.1039/c7cp05726a.
Using X-ray reflectivity, spectroscopic ellipsometry and Raman spectroscopy, we have studied the stratified structure and the two glass-like thermal transitions in sufficiently aged glassy polystyrene films. We find that favorable interaction between the solid substrate and the polymer film induces stratification within the film resulting in different densities across the film thickness. Existence of two glass-like thermal transitions (one at 70 °C and the other at 95 °C) is independently confirmed by temperature dependent spectroscopic ellipsometry and Raman spectroscopy measurements. Interestingly, the thermal coefficient of expansion of the polymer film displays anomalous behavior with temperature and is found to have the lowest value over the temperature range 70-95 °C, i.e. between the two observed glass-like thermal transition temperatures.
利用X射线反射率、光谱椭偏仪和拉曼光谱，我们研究了充分老化的玻璃态聚苯乙烯薄膜的分层结构和两个类似玻璃的热转变。我们发现，固体基底与聚合物薄膜之间的良好相互作用会在薄膜内引起分层，导致薄膜厚度方向上密度不同。通过与温度相关的光谱椭偏仪和拉曼光谱测量，独立证实了存在两个类似玻璃的热转变（一个在70℃，另一个在95℃）。有趣的是，聚合物薄膜的热膨胀系数随温度呈现异常行为，并且发现在70 - 95℃的温度范围内，即在两个观察到的类似玻璃的热转变温度之间，其值最低。
